Shakespeare was the most powerful literate and eloquent writer of his time. He must have written throughout his life on a daily basis. As soon as a consigner gives away his letters or any written texts he looses control of it, and he never can be sure where his "words, poems, texts " will remain later on.---
The fact that not a singular rudiment of a (hand)written document from Shakspeare has ever been found needs a rational, scientific explanation, it is virtually impossible and can never become plausible. There must be a logical and plausible explanation for this "impossibility": Under no circumstances a complete lack of handwritten information of Shakespeare, having lived for a quarter of a century in London, may have happened. An answer by an expert: "I have no idea why it happened but it happened" is totally unacceptable and unscientific.
Can you think of a great composer, who left no handwritten notations?- Shakespeare must have left letters and writings in abundance. The most plausible possibility or explanation: The poet and dramatist did not write under the name we are looking for but used various peseudonyms and initials.. (s. --> Handwritings)
The most often used argument that we do not have handwritten material from so many other contemporous writers either, means that the cat bits into its own tail. If we start to notice that our poet used dozens and dozens of pseudonyms and initials during his long lifetime (like Willobee, -->Clarke, -->Griffin, -->Barnfield, -->Davison, -->Breton, -->Markham, -->Basse, -->Taylor, -->Chapman, -->Heywood, ->Drayton etc.etc, absurd though it might sound) it becomes clear that you will not find handwritten material from many of those, similar to Shakspere.